linux-sysctl-defaults: Increase vm.max_map_count to 1048576
The kernel default value of vm.max_map_count is 65530, which ensures
that ELF core dumps can use the original 16-bit section numbering.
However, some Windows games use far more mappings than this, and some
memory allocators might do so as well.
Since 2010 both the kernel and gdb support extended section numbering
which removes the 16-bit limit. So it seems quite safe to increase
vm.max_map_count beyond this value now.
Increase it to 1048576 (= 2^20), matching the value now used in several other distributions:
- https://archlinux.org/news/increasing-the-default-vmmax_map_count-value/
- https://fedoraproject.org/wiki/Changes/IncreaseVmMaxMapCount
- https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2057792
Closes: #1076510